We report theoretical investigations on the complexation and liquid-liquid extraction of trivalent lanthanide cations by picolinamide ligands L. The relative contributions of pyridine vs. amide moieties of L and the effect of alkyl substituents are investigated in the gas phase by quantum mechanical calculations. The uncomplexed ligands L with different lipophilic substituents and Eu(NO(3))(3)L(3) complexes are simulated at a water-"oil" interface, where "oil" is modeled by chloroform. The simulations point to the importance of interfacial phenomena in the liquid-liquid extraction of cations by picolinamide ligands and the difference between pyridine vs. amide substituted ligands.